Direct imaging of hydrogen-atom columns in a crystal by annular bright-field electron microscopy
Direct imaging of hydrogen-atom columns in a crystal by annular bright-field electron microscopy
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DOI：
10.1038/nmat2957
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发表时间：
2011-04-01
期刊：
影响因子：
41.2
通讯作者：
Abe, Eiji
中科院分区：
文献类型：
--
作者：
Ishikawa, Ryo;Okunishi, Eiji;Abe, Eiji
增强显微镜的成像能力以识别从低原子序数到高原子序数元素的所有化学类型的原子，将为直接确定材料结构做出重大贡献。电子显微镜已经成功地提供了重原子位置的图像，特别是通过环形暗场方法，但由于其散射能力较弱，轻原子的检测很困难。像差校正电子光学的最新发展显着提高了显微镜的性能，能够识别单个轻原子，例如氧、氮、碳、硼和锂。然而，除了在石墨烯膜上氢吸附原子的特定条件外，最轻的氢原子尚未被直接观察到。在这里，我们展示了晶体固体 YH2 中氢原子的首次直接成像，基于经典的“空心锥体”照明理论与最先进的扫描透射电子显微镜相结合。从像差校正显微镜参数导出的优化空心锥条件证实信息传输可以扩展到22.5 nm(-1)，这对应于约44.4 pm的空间分辨率。这些实验条件可以通过扫描透射电子显微镜中的环形明场成像根据互易性轻松实现，成功地将氢原子柱显示为暗点，正如弱相物体的相差所预期的那样。
Enhancing the imaging power of microscopy to identify all chemical types of atom, from low- to high-atomic-number elements, would significantly contribute for a direct determination of material structures. Electron microscopes have successfully provided images of heavy-atom positions, particularly by the annular dark-field method, but detection of light atoms was difficult owing to their weak scattering power. Recent developments of aberration-correction electron optics have significantly advanced the microscope performance, enabling identification of individual light atoms such as oxygen, nitrogen, carbon, boron and lithium. However, the lightest hydrogen atom has not yet been observed directly, except in the specific condition of hydrogen adatoms on a graphene membrane. Here we show the first direct imaging of the hydrogen atom in a crystalline solid YH2, based on a classic 'hollow-cone' illumination theory combined with state-of-the-art scanning transmission electron microscopy. The optimized hollow-cone condition derived from the aberration-corrected microscope parameters confirms that the information transfer can be extended to 22.5 nm(-1), which corresponds to a spatial resolution of about 44.4 pm. These experimental conditions can be readily realized with the annular bright-field imaging in scanning transmission electron microscopy according to reciprocity, revealing successfully the hydrogen-atom columns as dark dots, as anticipated from phase contrast of a weak-phase object.